In gas turbine engines, fuel is delivered from a fuel source to a combustion section where the fuel is mixed with air and ignited to generate hot combustion products that define working gases. The working gases are directed to a turbine section where they effect rotation of a turbine rotor. It has been found that the production of NOx gases from the burning fuel in the combustion section can be reduced by providing a portion of the fuel to be ignited downstream from a main combustion zone.
FIG. 1 illustrates a conventional combustor 112 of a can-annular combustion system included in a gas turbine engine 110. Pressurized air is mixed with fuel from main and pilot fuel injectors 166, 168 and ignited in a main combustion zone 143, creating combustion products comprising hot working gases 144. The combustor 112 further includes a secondary fuel stage 114 positioned at a secondary combustion zone 170 located downstream of the main combustion zone 143. The secondary fuel stage 114 includes nozzles 118 positioned to inject an air/fuel mixture into the secondary combustion zone 170. FIG. 2 illustrates conventional nozzles 118 used at the secondary combustion zone 170 of the combustor 112, with a single outlet to inject the air-fuel mixture.